In a mobile communication system, each base station transmits or receives data to or from a user equipment through one cell/sector in a wireless channel environment. In a system operated using multiple carriers or the like, a base station receives packet traffic from a wired Internet network and transmits the received packet traffic to each user equipment using a predetermined communication protocol. At this time, downlink scheduling includes determination as to when the base station transmits data, to which user equipment the data is transmitted, and which frequency region is used for data transmission. In addition, the base station receives and demodulates data from the user equipment using a predetermined communication protocol and transmits packet traffic through a wired Internet network. On the other hand, uplink scheduling includes determination as to when uplink data is transmitted to the base station, which user equipment transmits the uplink data, and which frequency band is used for uplink data transmission. In general, scheduling is performed such that a user equipment with a good channel status transmits or receives data using more time and frequency resources.
FIG. 1 is a diagram explaining time-frequency resource blocks. A resource used in communication in a system operated using multiple carriers or the like may be divided into a time domain and a frequency domain. The resource may be defined by Resource Blocks (RBs) and each RB includes N subcarriers and M subframes or a predetermined time unit. At this time, N and M may be 1. One rectangle shown in FIG. 1 denotes one RB, and one RB includes at least one subcarrier located on one axis and a predetermined time unit located on the other axis. In downlink, the base station selects a user equipment according to a predetermined scheduling rule, allocates one or more RBs to the selected user equipment, and transmits data to the selected user equipment using the allocated RBs. In uplink, the base station selects a user equipment and allocates one or more RBs to the selected user equipment according to predetermined scheduling rule. The user equipment receives scheduling information indicating that the base station has allocated certain RBs to the user equipment and transmits uplink data using the allocated RBs.
In the downlink scheduling scheme, the base station selects time-frequency RBs with a good channel status based on a downlink Channel Quality Indicator (CQI) reported by the user equipment and transmits data using the selected RBs. Since the time-frequency RBs with the good channel status are used, it is possible to transmit a larger amount of data while using restricted RBs. Thus, it is possible to increase overall data transfer capacity of the system. In the uplink scheduling scheme, a scheduler of the base station may measure the reception status of a pilot signal or a reference signal transmitted from the user equipment and select and allocate time-frequency RBs with a good uplink channel status to the user equipment. The user equipment may transmit uplink data using the allocated RBs.
Unicast service control information includes user-specific control information and non-user-specific control information. The non-user-specific control information may include information for enabling a user equipment to decode user-specific control information such as the size of user-specific control information.
Provided that user-specific control information is comprised of control information for user(s), the user-specific control information is further divided into resource assignment information, power control information, and Hybrid Automatic Repeat reQuest (HARQ) ACK/NACK feedback information. HARQ ACK/NACK feedback information for uplink data transmission is transmitted through a downlink ACK channel, and is distinguished from a control block of other user-specific control information.
In order to allocate resources to one or more user equipments contained in one group, group control information may be used. In this case, control information may be configured in the form of an A-MAP (Advanced-MAP). In association with intended user-specific control information of user(s), multiple information elements are respectively coded, and are masked with Cyclic Redundancy Check (CRC) of the A-MAP using UE IDs (including STID, broadcast STID, and multicast STID of each UE). Since A-MAP is separately encoded and masked with an STID, a UE performs blind detection of the A-MAP transmission region so as to determine the presence or absence of A-MAP to be transmitted to the UE. In this case, the UE may use STID, broadcast ID, and multicarrier ID (e.g., group ID, persistent ID, Sleep/Idle mode ID, MBS ID, etc.) that are assigned to the UE.
The UE may perform blind detection on the basis of the size of MAP used in the corresponding system, and may limit the MAP size to a predetermined size and also limit the type such that the number of blind detections is reduced. For example, the size of A-MAP IE (Information Element) may be limited to three types (for example, 56 (or 64), 96, and 144) or two types (for example, 56 (or 64), and 96). It is assumed that, when one minimum logical resource unit (MLRU) is composed of 48 data subcarriers or 2 MLRUs are composed of 96 data subcarriers, the size of A-MAP IE is set to 56 or 96. At this time, using the encoding method (e.g., tail-biting convolution code (TBCC) and puncturing) for a downlink control channel, A-MAP IE of 56 bits may be mapped to one MLRU, and A-MAP IE of 96 bits may be mapped to two MLRUs.
The above-mentioned scheduling may be carried out on a group basis.
Group resource allocation (GRA) technology allocates resources to multiple users contained in one group so as to reduce overhead of a control message that is transmitted from a BS to a UE. In the case of using the group resource allocation technology, resources are separately assigned to each UE, resource allocation position information (e.g., resource start offset and resource size), an MCS level of burst, etc. are compressed and transmitted to UEs, resulting in reduction in overhead of control information.
FIG. 2 is a diagram showing an example of a group resource allocation (GRA) method using bitmaps.
Referring to FIG. 2, bitmaps may be used to notify the UEs belonging to a predetermined group of resource allocation information. A user bitmap which is a first bitmap indicates which of mobile stations belonging to a specific group corresponding to the bitmap is scheduled at a time corresponding thereto. Each bit of the user bitmap corresponds one-to-one to each of UEs belonging to the group. In FIG. 2, one group may include six users at maximum. Each bit of the user bitmap set to “1” indicates a user (that is, a user, to which resources are allocated) currently scheduled in a frame.
FIG. 2 shows that first, second, fourth and sixth users are scheduled in an n-th frame (Frame n). Each UE may acquire information about its location in a group when being added to the group through a user bitmap received from the base station. Next, a resource allocation bitmap indicates resource allocation information of the scheduled users and the resource allocation information may include information such as an MCS (Modulation and Coding Scheme) level and the size of allocated resources. In FIG. 2, since information about one UE may be expressed by 3 bits and a total of four UEs are scheduled in the n-th frame, the size of the resource allocation bitmap becomes 12 bits (3×4). Since five UEs are scheduled in an (n+p)-th frame (Frame n+p), a resource allocation bitmap having a total size of 15 bits is formed.
The persistent allocation (PA) will hereinafter be described in detail.
In the same manner as in VoIP in which packet transmission can be predicted, periodic traffic transmission need not perform burst allocation signaling (i.e., resource allocation for transmission) for each packet transmission. In this case, persistent allocation (PA) may be used. That is, persistent allocation (PA) having a relatively fixed payload size can reduce overhead generated when resources are assigned to connection or service(s) having a periodic pattern. The BS can periodically allocate resources using initially assigned resources without use of a separate MAP during a predetermined time, resulting in a reduction in MAP overhead.
Position, size, and MCS information of resources transferred by a persistent allocation MAP are maintained by a base station and UE until modification, deletion, or error occurs in resource allocation.
In order to perform persistent allocation (PA) on only one UE, a base station (BS) transmits a DL/UL individual persistent A-MAP to a UE. In order to simultaneously perform persistent allocation for multiple UEs, the base station transmits a DL/UL composite persistent A-MAP to the UE.
The group resource allocation (GRA) method and the persistent allocation (PA) methods are designed to allocate resources to each UE using different A-MAP IEs. If each A-MAP IE always has the same format, or if a UE to be scheduled does not exist or is changed to another, unnecessary resource consumption may occur.